The basophil, along with the mast cell, contains cytoplasmic granules with an affinity for basic dyes. The basophil is produced by the bone marrow and circulates in the blood. Basophils are associated with helminthic parasitic infections and allergic reactions and they possess a high affinity receptor for IgE antibodies. Little is known however about the proteins which comprise the granule, in part because, under normal conditions, basophils constitute less than 1% of peripheral blood cells and it is therefore difficult to obtain an adequate amount of purified material for study.
While some researchers have proposed that basophils are the precursors of mast cells, recent data suggests that basophils represent terminally differentiated leukocytes, possibly more closely related to eosinophils (Galli, S. J. and Lichtenstein, L. M., in Allergy:Principles and Practice, Middleton et al (Eds.), 3rd Ed, Vol. 1 (1988), pp 106-134).
Basophils appear to participate in many inflammatory, immunological and pathological reactions. For a general review see Galli et al, Prog Allergy (1984) 34:1. The most striking tissue infiltrates of basophils occur in cutaneous basophil hypersensitivity reactions (Galli and Askenase, in The Reticuloendothelial System:A Comprehensive Treatise, Abramoff et al (Eds.) pg 321, Plenum Press 1986). Recent studies suggest that basophils are essential for expression of immunity to the feeding of larval Amblyomma americanum ticks. Here, basophils may collaborate with eosinophils in the expression of immunity by acting to attract eosinophils into tissues where the eosinophils subsequently release toxic cationic proteins (Brown, S. J. et al, J Immunol (1982) 129:790). Basophils are also elevated during helminthic infections, suggesting that they might participate in host defense to these parasites (Ogilvie, B. M. et al, Immunol (1980) 39:385; Lindor, L. J., Parasite Immunol (1983) 4:13; Juhlin, L. and Michaelsson, G., Lancet (1977) ! :1233). Evidence also exists that basophils function in hypersensitivity reaction (Schwartz, L. B. and Austen, K. F. in Immunological Diseases, Samter et al (Eds) Little Brown & Co 4th Ed, pg 157 (1988); Mitchell, E. B. Clin Rev Allergy (1983) 1:427), and in IgE mediated cutaneous late phase reactions (Solley, G. O. et al, J Clin Invest (1976) 58:408; Charlesworth, E. N. et al, J Clin Invest (1989) 83:1519).
Studies of human basophil granule proteins have been limited by the difficulty of obtaining sufficient numbers of basophils because they constitute only about 0.5% of the total leukocyte population. Prior studies of proteins isolated from the basophils of guinea pigs repeatedly immunized with sheep blood revealed a mixture of neutral esterases-proteases and both trypsin and chymotrypsin-like serine hydrolases, Dvorak, H. F. et al, J Immunol (1974) 113:169; J Immunol (1977) 119:38. Studies of the glycosaminoglycans (GAG) of these proteins showed a mixture of GAGs including chondroitin sulfate, dermatin sulfate, and small amounts of heparin sulfate (Orenstein, N. S. et al, J Immunol (1978) 121:586).
Several proteins have been localized to the human basophil granule including the eosinophil major basic protein (Ackerman, S. J. et al, J Exp Med (1983) 158:946) and the Charcot-Leyden crystal protein (Ackerman, S. J. et al, J Exp Med (1982) 155:1597). In addition, mast cell tryptase can be identified in human basophils at about 40 pg/cell, a level roughly 500-fold lower than in human mast cells (Casteils, M. C. et al, J Immunol (1987) 138:2184). In addition, bradykinin generating activity has been ascribed to basophils by virtue of the release of this enzyme from peripheral white blood cells by IgE dependent stimulation (Newball, H. H. et al, J Clin Invest (1979) 64:466).
The present invention was facilitated by a patient that presented with basophilic leukemia. Leukocyte counts were over 10.sup.5 cell/.mu.l and contained 78% basophils. On two occasions this patient underwent cytophoresis for removal of leukocytes and a total of 1.5.times.10.sup.11 basophils were obtained. Examination of the granule proteins of these basophils have revealed a number of novel proteins with unique N-terminal amino acid sequences.